UI Extension Master Gardeners UI Extension Events UI Extension Idaho Landscapes and Gardens Seasonal Topics UI Extension Idaho Landscapes and Gardens Get Answers UI Extension Idaho Landscapes and Gardens UI Extension Idaho's Growing Regions University of Idaho Extension UI Extension Idaho Landscapes and Gardens UI Extension Idaho Landscapes and Gardens Image Map
Aug 162012

Most weed problems in lawns are associated with a weak, thin turf. A thin turf is easily pushed aside by aggressive weeds which can become worse over time. Make sure to follow good fertilization, irrigation and mowing guidelines to build a thick, vigorously growing lawn. Heavy weed populations are usually an indication of some other inherent problem with the lawn.

Some perennial weeds, like white clover, can still become problems even in well managed lawns. Many herbicides are available to effectively control weeds in lawns, but their success largely depends on proper application, and perhaps more importantly, on correct timing. Knowing what weeds you have will help you determine the best time of the year to control them.

Realize that it is impossible to eradicate all weeds from a lawn even with herbicide use. Learn to tolerate some weeds in your lawn and avoid indiscriminate use of herbicides which can injure trees, surrounding landscape plants and even the lawn itself.

Photographs of many weeds can be found at WSSA’s Photo Gallery.

Perennial Broadleaf Weeds

Some common perennial broadleaf weeds in home lawns include dandelion, field bindweed (also called morningglory), white clover, curly dock, ground ivy, Canada thistle, broadleaf plantain, buckhorn plantain and yarrow. Make sure to properly identify the weeds before choosing herbicides for control. University of Idaho extension educators, master gardeners and nursery personnel can help you with correct identification.

Broadleaf weeds can be controlled with postemergence herbicides (a chemical that is applied to weeds after the weeds have emerged from the soil) which kill weeds that are actively growing. Postemergence herbicides do not prevent weeds from germinating.

The best time of the year to control perennial weeds is in late summer or early fall when the weeds are preparing for winter. In preparation for winter, perennial weeds move energy reserves from the leaves to underground stems and roots, so a herbicide application at this time will ensure movement of the herbicide to these plant parts, thus resulting in a more effective kill because the roots are being affected. Spring applications to perennial weeds can slow their growth and may kill them, but it is more difficult. Regardless of when applications are made, make sure the weeds are actively growing at time of application. Avoid mowing for 1 to 2 days before and after the application to ensure maximum uptake of the herbicide by the weeds.

There are many broadleaf weed control products available for home use. These products will contain one or a combination of the following chemicals: 2,4-D, 2,4-DP, MCPP, MCPA and dicamba. They are safe to use on cool-season lawn grasses. Liquid and granular formulations of these chemicals are available. It is very important to properly calibrate sprayers or granular spreaders to ensure accurate, uniform application and avoid spraying adjacent flower beds or susceptible plants. Be sure to read and follow all label directions.

Perennial Grassy Weeds

Perennial grassy weeds are the most difficult weeds to control in a home lawn. Some common perennial grassy weeds include quackgrass, roughstalk bluegrass, smooth bromegrass, annual bluegrass (there exist some perennial biotypes) and even other cool-season grasses such as tall fescue and creeping bentgrass. There are essentially no herbicides available for the selective control of these weeds in a lawn. Removal of these problem weedy grasses prior to establishing a lawn and the use of high quality seed or sod is essential to preventing these weeds from becoming a problem. Many home lawns are established with poor quality seed that has high amounts of weeds such as annual bluegrass and roughstalk bluegrass. What is contained in a seed lot you are considering to purchase is readily available on the seed label, but most homeowners are unaware of its importance. If small patches of perennial grasses are found in a lawn, physical removal with a shovel or spraying with a non-selective herbicide such as glyphosate is the only option followed by re-seeding or sodding the bare areas.

Annual Grassy Weeds

Weeds like crabgrass and foxtail are warm-season grasses that germinate from seed in the spring and infest lawns during the hot days of summer. They tend to invade lawns along sidewalks and driveways where temperatures are hottest and lawns are thin. Thick, vigorously growing lawns will out-compete most annual grassy weeds.

Annual grassy weeds are best controlled with pre-emergence herbicides (a chemical that is applied before the seeds have germinated) which kill germinating weeds. These herbicides must be applied well before the weeds germinate since they will not kill weeds once they have emerged. Additionally, some of these pre-emergence herbicides are impregnated on fertilizer granules and applied as a weed and feed. Crabgrass will germinate when soil temperatures reach 55 to 60º F. This occurs around mid-March to early April for the Treasure Valley, Magic Valley and northern Idaho and late March to mid-April for central and eastern Idaho.

There are some herbicides that will kill young annual grasssy weeds, but they usually only work well on very young plants so application timing is critical.

Do not overseed into areas that have recently been treated with pre-emergence herbicides because the chemical will kill emerging lawn grasses as well. Check the label of the herbicide to see how long you need to wait before planting into an area treated with a pre-emergence herbicide.

 August 16, 2012
Aug 092012

Pesticides are an effective tool for combating numerous problems encountered in the home landscape and garden. When used properly they can save time and labor. Used improperly, however, pesticides can cause damage to plants, people and the environment. It is very important to read and understand the label on any pesticide container. In fact, the label is the law. Keep in mind that all pesticides are potentially poisonous and that improper application or use can be dangerous.

Warning Pesticide Use signThere are several categories of pesticides, and numerous products, available for use in the home garden. Herbicides can be used to control weeds. Some products will kill all vegetation and should be used only where no desirable plants reside. There are a small number of these products that sterilize the soil and prevent growth of any plants for several years. Products that sterilize the soil may also damage nearby trees and shrubs if the roots grow into or are already located in the treated area. Be sure you understand the nature and limitations of any compound applied. Some herbicides can kill seeds as they germinate but do not affect growing plants that are already growing. These can be used to control weeds around shrubs, trees or emerged garden plants. Other herbicides kill only certain types of plants, such as grasses. These can be used to control grass weeds in broadleaf garden plots, or their opposite counterparts can be used to control broadleaf weeds, such as dandelion, in lawns. In a garden, herbicides can make weed management easier, but cannot completely replace hand weeding.

The intended use of insecticides is to kill destructive insects and are often very important for managing garden pests. However, because these compounds are designed to kill animal pests, they are often the most toxic and damaging to the environment of all classes of pesticides. Insecticides can also kill beneficial insects so it is again important to read the label to avoid killing insects that help you out in the war against damaging insects. Insecticides should be used only when needed and then only when using all appropriate precautions.

Fungicides and bactericides are used to control plant diseases and can save your lawn, garden, and landscape plants from disease when applied in a timely manner. For many diseases, fungicides must be applied to the target plants before the disease appears. Consequently, they are often used in a preventative fashion.

For further information on pesticides, please refer to the following links:

For detailed general information on controlling pests in gardens, see chapters 9 – 14 in the Idaho Master Gardener’s Handbook.

For general instruction on reading labels and using pesticides in the home garden, see the following informative University of Idaho publication: Pesticides for the Home Garden and How to Use Them

See the EPA document Citizen’s Guide to Pest Control and Pesticide Safety for a comprehensive treatment of pesticide selection, management, and safety.

View a comprehensive database of pesticide products for home use from the Household Products site.

Purdue University has published A Strategy for Pest Control in Home Gardens outlining non-pesticide strategies for pest control.

For information on storing and disposing of pesticides, follow this link to an informative University of Idaho publication, Idaho Homeowner’s Commonsense Guide to Pesticides.

 August 9, 2012